Wafer processing reactor systems and methods are widely used in the manufacture of semiconductors and integrated circuits. One particular type of wafer processing system utilizes chemical vapor deposition (CVD) to deposit films or layers on the surface of a substrate as a step in the manufacture of semiconductors and integrated circuits. A variety of different CVD systems are used in the art. For example, films may be deposited using low pressure CVD (LPCVD) systems, atmospheric pressure CVD (APCVD) systems or different types of plasma enhanced CVD (PECVD) systems. In general principle, all such systems employ a deposition chamber where certain injected gaseous chemicals react and deposit a layer of material on the surface of the substrate. Many types of materials may be deposited, with dielectrics such as oxides and doped oxides being a typical example.
For proper operation of the system, and in particular to deposit a film of desired quality and repeatability, the flow of the gases within the reactor is important. Specifically, it is desirable to achieve a substantially uniform flow of gases in the area proximate the surface of the substrate so that certain concentrations of the gaseous chemicals or reactants are available at the surface of the substrate so that a proper film is deposited. Moreover, control of the flow of such gases will promote more efficient utilization of the gases for reaction.
Another important criterion when depositing films is the thickness uniformity of the film. It is desirable to achieve a film of substantially uniform thickness over the entire surface of the substrate. This endeavor becomes even more important as the diameter of substrates continues to increase. The flow of the reactive gases within the chamber plays an important role in the resulting film thickness. Thus, it is desirable to control the flow rate of the gases and to promote substantially uniform flow of the reactive gases over the entire surface of the substrate.
A further consideration which warrants considerable attention in wafer processing systems is the minimizing of particles and contaminants that form in the reactor. Particulates and contaminants are caused mainly by the accumulation of unreacted and by-product gaseous chemicals and the formation of deposits (often called powder build-up) on the surfaces of the reactor. Such deposits are a large source of particles which can contaminate the films being deposited on the substrate. To remove the deposits the system must be taken offline and serviced. Contaminates and gaseous chemicals that accumulate in stagnant flow regions promote corrosion of the reactor and can severely reduce the longevity of the system, as well as contribute to the contamination problem. The flow of inert and reactive gases plays an important role in either promoting, or minimizing, the accumulation of unreacted and by-product gaseous chemicals, which determine, in part, the extent of the powder build-up. Thus, it is desirable to provide a system that promotes control of the inert and reactive gas flows to minimize accumulation and powder build-up.
It has been found that the control of the exhaust flow rate of the varies gases may be used to address the aforementioned concerns. Problems occur when the exhaust system of a reactor does not function properly. For example, if the exhaust flow rate is too high, the gases do not completely react and deposition on the surface of the substrate is hampered. Conversely, if the exhaust flow rate is too slow, the gas flows are undefined and accumulate in the chamber causing deposits to form on the chamber walls. Accordingly, it is desirable to provide a system and method that controls, or "meters," the exhaust flow of gases; that is, a system and method that achieves and maintains certain selected gas flow rate values within the system. Additionally, since powder build up does occur, it is desirable to provide a system and method which employs control means which accurately control the gas flows and do not deteriorate over time.
One prior art method described in U.S. Pat. No. 5,851,293 employs a system that controls flow fluctuations in an effluent downstream of a reactor to dampen fluctuations upstream in the reactor. This system also employs an abatement system which treats the effluent from the reactor. This system appears to only operate to dampen pressure fluctuations, and does not provide meaningful process feedback control of the gas flows in the upstream system because the downstream sensor does not maintain a constant relationship between pressure and flow due to clogging from powder accumulation. Moreover, this system does not provide a method of metering the flow rates of the various exhaust gases to achieve and maintain desired values of the inert and reactive gas flows within the chamber.
In another aspect, it has been found that loading and unloading of a reactor can cause transient disturbances, such as pressure disturbances, within the reactor. Thus, it is desirable to provide a system and method that controls and minimizes such disturbances.